Chemical treatment process and apparatus



` June 27;.1933.

H. L. woLLENBERG CHEMICAL" TREATMENT PROCESS AND APPARATUS Filed Dec. 15,v 1930 FIE E FIE- :L

INVENTOR. Har/y L Wo//enb rg Patented June 27, 1933 UNITED STATES PATaNT OFFICE j HARRY L. WOLLENBERG, O SAN FRANCISCO, CALIFORNIA, .ASSIGNOB T0 LONGVIEW FIBRE COMPANY, OF SAN FRANCISC, CALIFORNIA, A CORPORATION 0F DELAWARE CmICAL TREATMENT PROCESS AND APIPABATUS l i Application tiled December i8, 1930. Serial No. 502,701.

This invention relates generally to processes and apparatus for effecting chemical treatment of various fibrous materials. has particular application to treatment by chemical liquor at an elevated temperature and at a pressure above atmospheric, as Jfor example the treatment of wood chlps wlth chemical liquor in the manufacture of wood ul p IE the past it has been common to carry out chemical treatment of fibrous material by batch operations. For example in the manufacture of sulphate or kraft pulp, stationary or rotating digesters are charged with wood chips, Vtogether with the chemical treatment liquors. The charge is cooked at an elevated pressure and temperature until the pulp has been properly digested, after` which it is removed together with the spent liquor, and a new charge introduced. The objections to batch processes are obvious. For a plant of a given capacity the apparatus required is relatively large and bulky, and is comparatively expensive to install and maintain. In the effort to reduce installation and operating costs larger units have been introduced but they have been found to involve-increased difliculty in maintenance of uniform temperature and other conditions so that yield and yquality of product have been adversely affected by increased size of batch units. A large amount of skilled labor is required because of the many operations involved in-charging, cooking and discharging the digesters. Even with careful manual supervision, it is difficult to secure adequate control and-uni-- formity of products, because the essential conditions are not uniform throu hout the treatment vessel, and also because etermination of the optimum cooking condition depends upon inherently unsatisfactory methods of sampling and testing the pulp as it is being treated in the digesters. Thus it is not uncommon tosecure relatively low yield and quality of finished product, due to causes such as overcooking of part of the charge that receives excessive chemical treatment. Such prior processes have also been ineflicient and w uneconomical due to the tremendous amountl of vsteam required for a short interval at the beginning of the cooking operation, thus producing an uneconomical load for the asso'- ciated vboiler plants. A "relatively large amount of heat is also lost due to radiation losses from the large treatment vessels, and due to loss of steam` when the pulp and spent liquor are discharged from the vessels by blowing down the steam pressure. This loss by blowing down of steam pressure can be appreci ated when it is considered that the steam pressure in the cooking operation is usually carried out at about 100 pounds per square inch. The practice of blowing oi to reduce pressure in the cooking operation also causes a loss of chemical, and makes' it diilicult to segregate fixed gases from the remainder of the blowo.

In an effort to obviate the' disadvantages of-batch processes in the treatment of fibrous material, it has been proposed to devise apparatus operating continuously. To my knowledge no such continuous apparatus or process has proven commercially practical. Their failure is believed attributable to improper methodsofintroducing and removing the fibrous material, and to the absence of proper methods of control. Furthermore previous continuous methods have not properly impregnated the fibrous material with the treatment liquor prior to the cooking for the treatment of fibrous material where-p' by the fibrous material is introduced into' and removed, from the treatment chamber while Athe pressure within the treatment chamber is maintained above atmospheric.

It is a further object of theinvention to devise a treatment process of the above character which will secure .more uniform and higher quality products, which will require very little attention, and which will be relatively economical in the use of steam and understood that the appended claims are tol` be accorded a range of equivalents consistent with the state oi the prior art.

Referring to the drawing:

)Figure l is a side elevation in cross section,

illustrating apparatus suitable lor use in carrying out the process of my'invention.

ltiig. 2 is a cross sectional detail illus0 tratinp the lmechanism which ll prefer to utilize at the point where the treated nbrous material is expelled from the apparatus,.-

ln my invention in place oi treating` separate batches ol solids with chemical solun tions or liquors, ll cause the iibroue material to be treeted, together with the treating liep uor, to continually advance along; a predetermined path, while the chemical treatment progresses to completion. lA have Jlound that il fibrous material beine,7 subjected to chem- 4ical liquor is 'formed into a comparatively loned upwardly moving compact column, treatment at dillere'nt sections along the length oil this column can proceed independently ci the chemical actions along other sections. Thus in practice l continually supn ply hbrous material, such as wood chips, to the lower end of a relatively loingP upright treatment chamber. Material ol this column is subjected to the treatment liquor which is introduced into the column concurrently with and preierably at a pointer points aol-f jacent to, the introduction of chips. As the material progresses to the upper end ol the' chamberor to the point of delivery, the `pressure appliedis IQradnally decreased., and the chemical action proceeds to completion. lit the upper end oil the chamber the spent hquor and treated material areyremoved.- As will be presently explained, both for the introduction and for the removal ol the brous material from the treatment chamber or vessel, the material is compressed to form relal tively compact masses which serve as closures to maintain a pressure within the treatment chamber above atmospheric.

yReferring 'to the drawing for a concrete example of apparatus whichcan be utilized in my system, l have shown a digester or digesting container l0, which is positioned 11pneiaeia I .municating thru the bottom o right and which is relativel long compared to its cross sectional area. or continuously introducingl fibrous material to the lower portion of this chamber there is shown a rotatable screw 1l positioned within a suitable housing l2. A conduit 13, which can be substantially cylindrical, communicates between the discharge end of housing l2 and the bottom ol treatment chamber l0. A hopper le is illustrated lor-introducing chips or 'other brous material into housing l2.

Screw ll is preferably formed in such a manner that itis not only a feed means, but also a means for compressing the ber to a relatively compact mass. 'lhus as-illustrated in the drawing the screw ll is provided with a gradually decreasing pitch and is also tapered to lit the tapered housing l2. llt is also possible to utilize a screw oi proper design hav ing simply a continuously decreasing pitch without resorting to a tapered construction, a tapered construction can be utilized with constant itch, a tapered hub can be employed with e straight screw of constant` pitch, or various combinations ol these design factors can be utilized. `lhe results to be accomplished are the 'formation oi a compact column of brous material maintained at a relatively high pressure, which is conn tinuelly advanced thru conduit ll to the bottom ol treatment chamber l0., l have found that il such a plug or column within conduit'll is suiciently compact, it serves as an effective closure against pressure within the treatment chamber. ln other words although liquor under pressure may penetrate the plug to a certain imited extent, the friction oi"- 'ered by the relatively compact librous mass is so great that no liquor llow thru or about the mass will occur. Since the design of screws adapted to compress :dbrous material is well-known in the art, further disclosure concerning their construction is unnecessa llt may be pointed out however that for di erent operating conditions, as for exam le did'erent iibrous materials, the screws must e designed accordingly. y

'llhe treatment liquor is preferably introduced at the bottom of the treatment chamber l0, adjacent the point at which the brous material is introduced thru conduit i3. For this pur ose l have indicated pi i6 com-` treatment chamber l0. l

Various expediente can be utilized for heating the contents of chamber 10 to an elevated temperature. For' example l have indicated a plurality ol pipes 17 distributed along the length of the chamber. Fora purpose which. will be presently explained, the lowermost point of introduction'of steam or ap lication of heat is preferably spaced a su stantial distance above the bottom of the charnmr. Instead of directly injecting steam it is obl yious that steam jacketing canbe employed. l

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To minimize heat losses a jacket of heat insulating material 20 is shown. Arranged within the chamber I preferably provide means for continually breaking up the compact vmass of fibrous material as it is introduced, and for causing the fibrous material to progress toward the upper end of the chamber. Thus there is shown a, shaft 18 extending longitudinally of the chamber, and mounted at spaced points along this shaft are inclined blades or flights 19. Certain of the blades 19 are grouped near the lower end of the shaft 18, to break up or mechanically disintegrate the compact column of fibrous material being introduced into the chamber from conduit 13. In operation shaft 18 is slowly rotated in a direction to cause flight 19 to continually urge the fibrous mate- `lrial u wardl v 20 P Y The upper end of chamber 10 communicates with what can be termed a goose neck conduit 21, which forms` a wier 22. The treated fibrous material together with the spent treatment liquor flows over wier 22 to the .expelling means to be presently described,

thus causing the liquor and fibrous material to. maintain a substantially constant height within the treatment chamber.

The expelling means consists of a housing 23 in communication with conduit 21, and in which a rotatable screw 24 is disposed. Screw 24 is designed to have characteristics'similar to screw 11 previously described in that it serves to compress the fibrous material..

Housing 23 is provided with a perforated.

portion 26, which communicates with an outer` closedV liquor chamber 28. Pipe 29 communicates with chamber 28 for the removal of liquor, the pipe being provided with a valve 31, a trap, or equivalent device. Con

duit 32, which can be substantially c lindrical, is formed at the discharge end of ousing 23. For purposes to be presently explained a closure member 33 can be mounted adjacent the'outeiend of -conduit 32,'and the positoning of this closure 4member 33 can be controlled by a hydraulic piston and cylinder device 34 or equivalent means.

The expelling means described above receives spent liquor together with treated fiber fiowin over wier 22. As this mass is compresse by screw 24 liquor is expelled into chamber 28 and withdrawn thru pipe 29. A suliicient amount `of liquor is separated to enable the resulting mass to be compressed to form a compact column which is continually progressed outwardly thru conduit 32. This compressed mass is likewise suiciently compact to form a closure against the pressure-` within the treatment chamber. The de ee oipressure upon the mass being expelled t ru conduit 32 can be controlled thru practical limits by urging closure member 33 with more or less force towards thel conduit 32. Likewise when the apparatus Vis first started in operation, closure member 33 can be forced into engagement withconduit 32, to serve as a closure to retain pressure within the treatment chamber.

In operating my apparatus, fibrous mateintroduced thru pipes 16 is not sucient to immediately commence the cooking or digesting of the wood chips. Therefore .while a given strata of wood chips is progressing upwardly fromV the bottom of the chamber to the lowermost of steam pipes 17, the chips are being thoroughly impregnated with the treatment liquor. As the same strata con'- tinues tov progress 'upwardly thru the treatment chamber, the chips and treatment liquor are heated to an elevated temperature by the injection of steam, toy carry out the cooking ordigesting operation. By the time the same strata reaches the top of the treatment chamber positioned tp flow over wier 22, the cooking operation wi l have been completed,

and the material is then dischar ed by screw From time to time The relative proportions of liquor and fibrous material within the treatment chamber are referably such that a suiicient amountol) liquor is provided for the cooking operation, without providing such an excess as might cause-channeling within the chamber. In general I have found that the capacity of the apparatus is primarily determined by the dimensions of the cooking chamber, and therate of progress of the material thru the chamber. The temperature, and other factors must be such that cooking is complete when the'material reaches the top of the chamber. Screw 11 is then operated' at such a speed as to furnish the amount of material that can be thoroughly cooked under the conditions established. Screw 24 is operated at such a speed as to assure removal of all material' reaching it over wier 22, within the v liquor, means for heating nand spent liquor from the c y .5 adapted to be maintained under pressure greater than atmospheric and tovcontain a treating liquor,

means for continually introducing fibrous material into the lower portion of the chamber together with treatment chamber, means wier located adj l the chamber over which spent liquor and treated fiber are caused to flow to said expeiling. means.

the contents of said treated fiber amber, and a acent the upper portion of for `expellin 9. In apparatus ofthe character described, an upright elongated treatment chamber adapted to be `maintained under pressure 2 greater than atmospheric,

ally advancing fibrous material into the means for continua compressed column of chamber, said column being so compactas to serve as a closure against the the chamber, means liguor under pressure into the lower o the chamber, means integrating the inner end of the column o 'fibrous material pressure within for introducing tratmg ortion as it isadvanced intp the chamber whereby the treating liquor 1s enlower portion ofthe for mechanica ly dis-K trained with the brous materials and, is caused to progress in the form of a column upwardly thru the chamber, a wier located adjacent the upper ortion of the chamber over which treated ii r and entrained spent liquor is caused to ow, means for removing a substantial uantity of the entrained spent liquor from t e treated fibrous material, a conduit thru which the resulting treated fibrous material is adapted to be dlscharged, and means for dischargmg the treated fibrous material thru said condult in a compressed column so compact as to serve as an eiective closure against pressure within the chamber.

. 10. A continuous process for the treatment of fibrous material characterized by an elongated treatment chamber, said method comprisin continually progressing the fibrous matenal through said chamber in contact with treatment liquor maintaining the pressure within the chamber above atmospheric. and heating the material the same only travel throug the chamber, whereby durin the first part of its travel preimpregnation o the fibrous material will be elected under ,i pressure without substantial cooking. f In testimony whereof, I have hereunto set m .hand. y HARRY L. WoLLENBEaG.

to eect cooking ofL during the latter part of'its n ne 

